DC-coupled storage that pays back in about eight months

The background

The client already operated a 10.75 MWp on-grid PV plant and wanted to add storage with a smart dynamic-pricing function — capturing value from a volatile electricity market rather than simply exporting solar at low feed-in rates.

The challenge

On a price-volatile market, exporting midday solar leaves money on the table. The site needed storage that could trade energy across the day, on difficult Nordic terrain.

• Midday PV surplus was being exported cheaply instead of stored for high-price hours.
• The business case depended on charging at low prices and discharging when prices peak.
• Mountainous, forested Nordic terrain demanded a compact system that installs fast.

The solution

A DC-coupled architecture was chosen deliberately — it is the most efficient way to move existing PV energy into the battery.

In a DC-coupled design the battery and PV share inverter infrastructure, so the PV charges the battery directly through DC-to-DC conversion. That removes one conversion stage and its 2–4% loss, giving roughly 95–96% charging efficiency from PV.

The design supports up to 200% PV oversizing, capturing clipped energy that a smaller inverter would otherwise waste — and the system can charge the battery and feed the grid at the same time.

The 12.5 MWh is built from 125 × 50 kW / 100 kWh units — a modular, compact layout that is fast to install and well suited to constrained Nordic sites. Dynamic pricing logic charges at low prices and discharges to sell at peaks.